Over an addition 8 million. Then there are the special editions of the games for which there aren't any sales figures.

Also, there's a disparity in media. One is home media, and one is not. For example, a lot of people go and see films more than once, so that would need to be factored in for sales, whereas a game only needs to be bought once, then it can be replayed as many times as you want, it can be lent out, sold and resold, whereas film tickets can't.

A better example is when home media sales are compared to home media sales, in which Arkham suddenly holds up much, much better. The Arkham franchise all in all contains a little over 16 million sales. Now, The Dark Knight alone beats that with almost 18 million, but The Dark Knight Rises fares much worse, with only just scraping over 5 million sales. So combined TDK/R have 23 million sales compared to Arkham's 16, but that then means Arkham makes up over 75% of that same audience.

The films reach a wider one-time audience, but but in terms of pop culture conciousness, there isn't massive disparity in the long term impact between series. I'd also like to add Batman '89 outsold The Dark Knight Rises in ticket sales. But cross-media comparisons never work.

I hate to be that guy, but:

You write down, for example, that The Dark Knight sold 18 million units. Yeah, it sold 18 million DVDs... but that doesn't include the number of blu ray units, the number of digital copies sold, and international sales:http://www.the-numbers.com/movies/2008/BATM2.php
Oh yeah, and it doesn't include the platform sales for the platform known as the movie theatre. For that one, ~100,000,000 tickets were sold, implying at least ~50,000,000 viewers.

Whereas with Batman: Arkham Asylum, you are taking in total sales across every platform (which you're not doing for TDK), and you're including both domestic and international sales figures. That's why you have a less lopsided total, you are cherrypicking your statistics.

So even if we take the 7 million consumers of Arkham: Asylum, it still does not compare very well at all. It's still an obscure property. I'm glad you enjoy it, I'm glad a lot of people enjoy it, but to argue that the Batman movies should be structured as fan service to consumers of Arkham Asylum the video game is nonsense.